The invention relates to overload protection to avoid damage to optical components because of excessive light power from a light source, particularly to protect a glass fiber system used to transmit laser light.
The optical components or systems here to be protected from destruction by excessive light power are, for instance, glass fiber systems to transmit laser light to a measurement system. Such glass fiber systems are used in confocal microscopy, among other applications. Lasers which have great intensity differences among the individual lines, are often used, so that the total laser power must be set extremely high so that individual weak lines can also be excited. With such lasers, then, the total output power may be so high as to exceed the threshold for destruction of the glass fiber system. In any case, lasers with multiple wavelengths have high light power at the laser output, in the range of 2 to 3 watts. If the threshold for destruction of a glass fiber system is exceeded by the laser beam coupled into it, one speaks of the xe2x80x9cdeathxe2x80x9d of the fiber, as the fiber inlet is actually burned up.
The invention is, therefore, based on the problem of designing and developing overload protection to avoid damage to optical components by excessive light power from a light source, especially for protection of a glass fiber system used to transmit laser light, such that adequate protection of the optical components stressed by laser light is achieved with simple means and without turning off the light source. With respect to a glass fiber system as the optical component, burning of the fiber inlet should be avoided.
The overload protection according to the invention of the type under discussion here solves the problem stated above. According to that, the overload protection to avoid damage to optical components by excessive light power from a light source involves a means to couple out a small portion of the light, a detector to detect the intensity of the light coupled out, an electronic evaluation unit to compare the detected light intensity with a presettable maximum or threshold value, and a means to reduce the light power or to cut off the light incident on the optical component in case the maximum value is exceeded.
It is recognized according to the invention that the optical component can be protected by detecting the intensity or power of the light directly in its beam path; but here it is suggested that a small portion of the light be coupled out of the beam path. The small portion of the light coupled out is detected with respect to the light intensity and compared, in an electronic evaluation unit, with a preset maximum value. This maximum value must, obviously, refer to the ability of the optical component to carry a photooptical load. In the case of a laser being coupled into a light fiber, the maximum value of the light intensity or light power must be below a value that will damage the light fiber. Finally, the means to couple out the light, the detector, and the means to reduce the light power or to cut off the light incident on the optical component make up a control loop which then acts on the beam path directed onto the optical component if the preset maximum value for the light intensity is exceeded.
The means to reduce the light power or cut off the light incident on the optical component can act in various ways. For instance, it is possible for the means to reduce the light power to dim or throttle the light source directly or, in the extreme case, actually turn it off, in which case one can define a complete shutoff as xe2x80x9cemergency offxe2x80x9d. In a very particularly advantageous way, though, it is possible to design the means to reduce the light power as a filter placed between the light source and the optical component. It may also be a filter combination. This filter combination could, for example, comprise filter wheels or similar design measures. In any case, the filter or filter combination should assure that it is possible to reduce the light intensity or light power incident on the optical component, depending on the detected light power.
As part of an alternative embodiment, the means to reduce the light power could be designed as an acousto-optical filter (AOTF=acousto optical tunable filter) placed in the beam path between the light source and the optical component. Thus the primary light or laser beam would have its amplitude attenuated by the electronic control of the AOTF to an amplitude below the maximum value, and thus to a non-dangerous intensity value.
It is also conceivable for the means to reduce the light power to involve a mechanical shutoff unit, a shutter, between the light source and the optical component. If the maximum value established for the light intensity is exceeded, the primary light beam would be blocked by the mechanical shutter, thus assuring protection of the optical component with simple means.
As noted above, an out-coupling means which couples out a small proportion of the light incident on the optical component is provided for detection of the light intensity. This out-coupling means could be designed as a beam splitter. In an actual case it could be a thin glass beam splitter plate, that is, a thin glass plate. Such a thin plate is particularly suitable as a beam splitter, because such a plate, without any other coating, is already usable for partial reflection of about 4% to 6% of the incident light. A comparable range, from about 4% to 6%, preferably 5% of the light beam, should be coupled out for detection of the light intensity.
The out-coupling means and the means for reducing the light power could be combined into a structural unit in the beam path of the light in a particularly advantageous manner, especially with respect to compact construction. Both means can be arranged in a single housing which provides one light input and two light outputs, one for the primary light beam and another for the light coupled out.
It is also particularly important for the detector for detecting the light intensity or light power of the light coupled out to be calibrated with the split ratio, that is, primary light beam/out-coupled light, taken into consideration so as to be able to draw conclusions about the actual light intensity of the primary light beam.